18 June 2020 at 5:42 pm #574648
This image was taken by a friend a few days ago. He is a seasoned imager. The field is the Squid Nebula.
Of the two brightest stars in his image, one of them is very red. When imaged with an OIII filter it appears to have a ring around it. The other, non-red star appears normal. He says both star images appear normal in Ha.
He has found another image online, captured in the same wavelength, and the star looks normal. This link is to an image which shows how red the star is.https://www.astrobin.com/315318/?nc=all
Has anybody an explanation for what’s going on here please? He is confident the ring must be some sort of artifact, but it would be super if he’s got the discovery image of a red super-giant puffing off it’s outer shell.
Attachments:18 June 2020 at 7:23 pm #582648David SwanParticipant
Hi Alan. Thanks for posting this. I’m browsing through images of the star on Aladin. The star is so bright that unfortunately the star image is associated with artifacts in all the plates. I’m not saying your colleague hasn’t found something – we need further obs. But not from me I’m afraid – I’m at 55 degrees north and the summer solstice approaches!
BTW: North is left, East is down.18 June 2020 at 8:52 pm #582649David StrangeParticipant
Was the image captured with a reflector or refractor? If the latter, the ring may have been caused by the star showing excess infrared emission hence out of focus with respect to other stars. Advise him to take another image of the same star field, but this time refocus on the star with the ring. If that sharpens then all the others will look like planetary nebulae – proving the point!
David18 June 2020 at 11:34 pm #582651
That was my first thought but this is reported to be a narrow band image in [OIII]. Though perhaps it is possible that the filter leaks in the IR?
Robin18 June 2020 at 11:49 pm #582652
As here for example
OK for visual use but most of these would need an IR block with a CCD camera
Robin19 June 2020 at 9:23 am #582654
Many thanks folks, I’ll pass those comment back no and let you know what flows from that.
Sorry about all the rubbish lines in my first post. I don’t know why it’s done that.
Alan19 June 2020 at 2:38 pm #582662
He’s used a Baader 8.5nm CCD narrow band filter. The graph shows it is fairly transparent beyond 1,050nm.
Alan19 June 2020 at 4:14 pm #582665
Well the sensor would not have much sensitivity that far into the IR but the star in question is the bright (V mag 6.6) star V419 Cep / HD203380. It is spectral class M2i which will be about 3x brighter at 1000nm compared with in the visual so pretty bright where the filter is transparent.
Robin21 June 2020 at 2:21 pm #582669Grant PrivettParticipant
I have a Baader Oxygen filter which seemed to leak. I gave up using it because of it.
There may have been a faulty batch at some point.
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